This invention relates to doors which serve to open and close access openings formed in ventilating ducts.
The sheet metal ducts which distribute air in buildings for heating, cooling and ventilation are normally provided with access openings at various locations so that the interior of the ductwork is accessible. In order to prevent "chattering" and other objectionable noise in the vicinity of the access openings, current practice requires that the edge of each opening be equipped with a rigid metal frame which is bolted or otherwise fastened to the duct to reinforce the thin edge of the access opening. Each access opening is provided with a door which is normally held closed against the frame by one or more door latches.
The door itself must be able to withstand the duct pressures without chattering or otherwise generating excessive noise, and the door must also be effectively sealed to the duct in order to prevent leakage. Normally, the door is mounted on the outside of the duct where the duct pressure tends to break the seal between the door and duct. As a result, it is necessary to either tolerate air leakage or provide elaborate and expensive seals along with door latches which are capable of holding the door tightly closed on its seal against the force exerted by the air pressure in the duct.
The need for a special metal frame around each access opening and complicated seals and latches for each door has significantly increased the costs of the ductwork. The overall expense can be readily appreciated when it is recognized that the ducts in a single building each have a large number of access doors. It is thus apparent that a need exists for an access door which is more economical than those that are currently in common use.